--- /dev/null
+#!/usr/bin/python3
+
+"""
+
+Proof-of-concept systemd environment generator that makes sure that bin dirs
+are always after matching sbin dirs in the path.
+(Changes /sbin:/bin:/foo/bar to /bin:/sbin:/foo/bar.)
+
+This generator shows how to override the configuration possibly created by
+earlier generators. It would be easier to write in bash, but let's have it
+in Python just to prove that we can, and to serve as a template for more
+interesting generators.
+
+"""
+
+import os
+import pathlib
+
+def rearrange_bin_sbin(path):
+ """Make sure any pair of …/bin, …/sbin directories is in this order
+
+ >>> rearrange_bin_sbin('/bin:/sbin:/usr/sbin:/usr/bin')
+ '/bin:/sbin:/usr/bin:/usr/sbin'
+ """
+ items = [pathlib.Path(p) for p in path.split(':')]
+ for i in range(len(items)):
+ if 'sbin' in items[i].parts:
+ ind = items[i].parts.index('sbin')
+ bin = pathlib.Path(*items[i].parts[:ind], 'bin', *items[i].parts[ind+1:])
+ if bin in items[i+1:]:
+ j = i + 1 + items[i+1:].index(bin)
+ items[i], items[j] = items[j], items[i]
+ return ':'.join(p.as_posix() for p in items)
+
+if __name__ == '__main__':
+ path = os.environ['PATH'] # This should be always set.
+ # If it's not, we'll just crash, we is OK too.
+ new = rearrange_bin_sbin(path)
+ if new != path:
+ print('PATH={}'.format(new))
--- /dev/null
+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
+<!ENTITY % entities SYSTEM "custom-entities.ent" >
+%entities;
+]>
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2017 Zbigniew Jędrzejewski-Szmek
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="systemd.environment-generator" xmlns:xi="http://www.w3.org/2001/XInclude">
+ <refentryinfo>
+ <title>systemd.environment-generator</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Zbigniew</firstname>
+ <surname>Jędrzejewski-Szmek</surname>
+ <email>zbyszek@in.waw.pl</email>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd.environment-generator</refentrytitle>
+ <manvolnum>7</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd.environment-generator</refname>
+ <refpurpose>Systemd environment file generators</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <cmdsynopsis>
+ <command>&systemenvgeneratordir;/some-generator</command>
+ </cmdsynopsis>
+ <cmdsynopsis>
+ <command>&userenvgeneratordir;/some-generator</command>
+ </cmdsynopsis>
+
+ <para>
+ <literallayout><filename>/run/systemd/system-environment-generators/*</filename>
+<filename>/etc/systemd/system-environment-generators/*</filename>
+<filename>/usr/local/lib/systemd/system-environment-generators/*</filename>
+<filename>&systemenvgeneratordir;/*</filename></literallayout>
+ </para>
+
+ <para>
+ <literallayout><filename>/run/systemd/user-environment-generators/*</filename>
+<filename>/etc/systemd/user-environment-generators/*</filename>
+<filename>/usr/local/lib/systemd/user-environment-generators/*</filename>
+<filename>&userenvgeneratordir;/*</filename></literallayout>
+ </para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+ <para>Generators are small executables that live in
+ <filename>&systemenvgeneratordir;/</filename> and other directories listed above.
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will
+ execute those binaries very early at the startup of each manager and at configuration
+ reload time, before running the generators described in
+ <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ and before starting any units. Environment generators can override the environment that the
+ manager exports to services and other processes.</para>
+
+ <para>Generators are loaded from a set of paths determined during compilation, as listed
+ above. System and user environment generators are loaded from directories with names ending in
+ <filename>system-environment-generators/</filename> and
+ <filename>user-environment-generators/</filename>, respectively. Generators found in directories
+ listed earlier override the ones with the same name in directories lower in the list. A symlink
+ to <filename>/dev/null</filename> or an empty file can be used to mask a generator, thereby
+ preventing it from running. Please note that the order of the two directories with the highest
+ priority is reversed with respect to the unit load path, and generators in
+ <filename>/run</filename> overwrite those in <filename>/etc</filename>.</para>
+
+ <para>After installing new generators or updating the configuration, <command>systemctl
+ daemon-reload</command> may be executed. This will re-run all generators, updating environment
+ configuration. It will be used for any services that are started subsequently.</para>
+
+ <para>Environment file generators are executed similarly to unit file generators described
+ in
+ <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ with the following differences:</para>
+
+ <itemizedlist>
+ <listitem>
+ <para>Generators are executed sequentially in the alphanumerical order of the final
+ component of their name. The output of each generator output is immediately parsed and used
+ to update the environment for generators that run after that. Thus, later generators can use
+ and/or modify the output of earlier generators.</para>
+ </listitem>
+
+ <listitem>
+ <para>Generators are run by every manager instance, their output can be different for each
+ user.</para>
+ </listitem>
+ </itemizedlist>
+
+ <para>It is recommended to use numerical prefixes for generator names to simplify ordering.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+
+ <example>
+ <title>A simple generator that extends an environment variable if a directory exists in the file system</title>
+
+ <programlisting># 50-xdg-data-dirs.sh
+
+<xi:include href="50-xdg-data-dirs.sh" parse="text" /></programlisting>
+ </example>
+
+ <example>
+ <title>A more complicated generator which reads existing configuration and mutates one variable</title>
+
+ <programlisting># 90-rearrange-path.py
+
+<xi:include href="90-rearrange-path.py" parse="text" /></programlisting>
+ </example>
+
+ <example>
+ <title>Debugging a generator</title>
+
+ <programlisting>SYSTEMD_LOG_LEVEL=debug VAR_A=something VAR_B="something else" \
+&systemenvgeneratordir;/path-to-generator
+</programlisting>
+ </example>
+ </refsect1>
+
+ <refsect1>
+ <title>See also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+</refentry>
projects / thirdparty / systemd.git / commitdiff
